Streptavidin, a bacterial protein isolated from Streptomyces avidinii, is similar to egg-white avidin in its strong affinity for biotin. It is used as a replacement for egg-white avidin because of its more favorable chemical properties. Unlike egg-white avidin which has a net positive charge at neutral pH and contains about 7% carbohydrate, streptavidin has almost no net charge at neutral pH, does not contain carbohydrate, and exhibits lower non-specific background.

All conjugates of streptavidin are recommended for use with Biotin-SP-conjugated affinity-purified secondary antibodies and Biotin-SP-conjugated ChromPure proteins. Compared with the avidin-biotin-HRP complex (ABC), HRP-conjugated streptavidin is more stable, gives less background, and is more sensitive as reported by Shi et al. (J. Histochem. Cytochem. 1988. 36, 317) and Milde et al. (J. Histochem. Cytochem. 1989. 37, 1609). The increased sensitivity may be due to enhanced tissue penetration and less steric hindrance, since nominal molecular weights for all components of the conjugated streptavidin system are less than 200,000, which are considerably lower than that of ABC.

We offer a comprehensive list of fluorophores and enzymes conjugated to streptavidin for use in enzyme immunoassays, immunohistochemistry, flow cytometry, in situ hybridization, and immunoblotting procedures. Most streptavidin products are freeze-dried in buffer containing stabilizers and preservatives.